Styrene is a useful monomer which polymerizes with itself and with other monomers to form useful materials for fabricating numerous household and industrial articles of manufacture. In shipping or storing the monomer it must be inhibited with one or another known inhibitors. Among these are p-tert.-butylcatechol, hydroquinone, and the methyl ether of hydroquinone. The p-tert-butylcatechol is most commonly employed as a storage inhibitor. It does not however, prevent polymerization of styrene which vaporizes in the space above the bulk liquid styrene and subsequently condenses on surfaces of the tank structure, such as support and reinforcing beams or girders and protruding bolts or rivets. Other structures such as nozzles, flame arrestors, relief valves, and vapor lines also provide condensing surfaces associated with the tank. This condensed material contains little or none of the inhibitor present in the bulk liquid monomer and thus polymerizes on these surfaces, often growing to large stalactite-like accumulations.
This polymer formation fouls the roof structure, vents, nozzles and instrumentation in the tank. It also amounts to a loss of monomer and when the bulk monomer contacts it, it dissolves in the monomer, resulting in a reduction of quality of the monomer. Before such monomer can be used or sold it must be purified to remove the polymer.
Various methods have been tried for minimizing the problem of the polymerization of the condensate. The tank roof has been painted to provide a less adherent surface and to cause the condensate to run off more rapidly into the liquid which contains inhibitor. Tanks have been built with minimal internal roof support structures. Heat has been applied to nozzles and vapor lines to prevent condensation.
At present the best solutions to the problem as practiced by the industry include painting the tank interior roof and eliminating internal support structures. None of these has proven entirely satisfactory.
It would be highly desirable to find a way in which the condensing monomer in large storage tanks and associated structures could be prevented from polymerizing on the insides of such tanks and structures.
It has now been discovered that if certain inhibitors are added to a coating used to cover these internal tank surfaces, they will be leached out by the condensed monomer and prevent the polymerization of the monomer on the internal surfaces of the tank.